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noMisrefactoredShorthandAssign

src/content/docs/linter/rules/no-misrefactored-shorthand-assign.mdx

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import { Tabs, TabItem } from '@astrojs/starlight/components';

<Tabs> <TabItem label="JavaScript (and super languages)" icon="seti:javascript"> ## Summary - Rule available since: `v1.3.0` - Diagnostic Category: [`lint/suspicious/noMisrefactoredShorthandAssign`](/reference/diagnostics#diagnostic-category) - This rule is **recommended**, meaning it is enabled by default. - This rule has an [**unsafe**](/linter/#unsafe-fixes) fix. - The default severity of this rule is [**error**](/reference/diagnostics#error). - Sources: - Same as [`misrefactored_assign_op`](https://rust-lang.github.io/rust-clippy/master/#misrefactored_assign_op)

How to configure

json
{
	"linter": {
		"rules": {
			"suspicious": {
				"noMisrefactoredShorthandAssign": "error"
			}
		}
	}
}

Description

Disallow shorthand assign when variable appears on both sides.

This rule helps to avoid potential bugs related to incorrect assignments or unintended side effects that may occur during refactoring.

Examples

Invalid

js
a += a + b
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-misrefactored-shorthand-assign">lint/suspicious/noMisrefactoredShorthandAssign</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Variable appears on both sides of an assignment operation.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>a += a + b <strong> │ </strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">This assignment might be the result of a wrong refactoring.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Use </span><span style="color: lightgreen;"><strong>a += b</strong></span><span style="color: lightgreen;"> instead.</span> <strong> 1 │ </strong>a<span style="opacity: 0.8;">·</span>+=<span style="opacity: 0.8;">·</span><span style="color: Tomato;">a</span><span style="opacity: 0.8;"><span style="color: Tomato;">·</span></span><span style="color: Tomato;">+</span><span style="opacity: 0.8;"><span style="color: Tomato;">·</span></span>b <strong> │ </strong> <span style="color: Tomato;">-</span><span style="color: Tomato;">-</span><span style="color: Tomato;">-</span><span style="color: Tomato;">-</span> </code></pre>
js
a -= a - b
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-misrefactored-shorthand-assign">lint/suspicious/noMisrefactoredShorthandAssign</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Variable appears on both sides of an assignment operation.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>a -= a - b <strong> │ </strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">This assignment might be the result of a wrong refactoring.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Use </span><span style="color: lightgreen;"><strong>a -= b</strong></span><span style="color: lightgreen;"> instead.</span> <strong> 1 │ </strong>a<span style="opacity: 0.8;">·</span>-=<span style="opacity: 0.8;">·</span><span style="color: Tomato;">a</span><span style="opacity: 0.8;"><span style="color: Tomato;">·</span></span><span style="color: Tomato;">-</span><span style="opacity: 0.8;"><span style="color: Tomato;">·</span></span>b <strong> │ </strong> <span style="color: Tomato;">-</span><span style="color: Tomato;">-</span><span style="color: Tomato;">-</span><span style="color: Tomato;">-</span> </code></pre>
js
a *= a * b
<pre class="language-text"><code class="language-text">code-block.js:1:1 <a href="https://biomejs.dev/linter/rules/no-misrefactored-shorthand-assign">lint/suspicious/noMisrefactoredShorthandAssign</a> <span style="color: #000; background-color: #ddd;"> FIXABLE </span> ━━━━━━━━━━━━━━━━━━━━━━━━━ <strong><span style="color: Tomato;">✖</span></strong> <span style="color: Tomato;">Variable appears on both sides of an assignment operation.</span> <strong><span style="color: Tomato;">&gt;</span></strong> <strong>1 │ </strong>a &#42;= a &#42; b <strong> │ </strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong><strong><span style="color: Tomato;">^</span></strong> <strong>2 │ </strong> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">This assignment might be the result of a wrong refactoring.</span> <strong><span style="color: lightgreen;">ℹ</span></strong> <span style="color: lightgreen;">Unsafe fix</span><span style="color: lightgreen;">: </span><span style="color: lightgreen;">Use </span><span style="color: lightgreen;"><strong>a &#42;= b</strong></span><span style="color: lightgreen;"> instead.</span> <strong> 1 │ </strong>a<span style="opacity: 0.8;">·</span>&#42;=<span style="opacity: 0.8;">·</span><span style="color: Tomato;">a</span><span style="opacity: 0.8;"><span style="color: Tomato;">·</span></span><span style="color: Tomato;">&#42;</span><span style="opacity: 0.8;"><span style="color: Tomato;">·</span></span>b <strong> │ </strong> <span style="color: Tomato;">-</span><span style="color: Tomato;">-</span><span style="color: Tomato;">-</span><span style="color: Tomato;">-</span> </code></pre>

Valid

js
a += b
js
a = a + b
js
a = a - b
</TabItem> </Tabs>